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  • International Union of Crystallography (IUCr)  (12)
  • BMJ Publishing  (1)
  • 1
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A time-of-flight small-angle diffractometer employing seven tapered collimator elements and a two-dimensional gas proportional counter was successfully utilized to collect small-angle scattering data from a solution sample of the lipid salt cetylpyridinium chloride, C21H38N+.Cl−, at the Argonne National Laboratory prototype pulsed spallation neutron source, ZING-P′. Comparison of the small-angle scattering observed from the same compound at the University of Missouri Research Reactor corroborated the ZING-P′ results. The results are used to compare the neutron flux available from the ZING-P′ source relative to the well characterized University of Missouri source. Calculations based on experimentally determined parameters indicated the time-averaged rate of detected neutrons at the ZING-P′ pulsed spallation source to have been at least 33% higher than the steady-state count rate from the same sample. Differences between time-of-flight techniques and conventional steady-state techniques are discussed.
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 311-319 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The resolution of a time-of-flight small-angle scattering spectrometer is complicated because many wavelengths contribute to the intensity for a particular scattering vector. The resolution function varies according to the wavelength distribution as well as with collimation. A rigorous calculation of the instrumental resolution requires averaging the resolution function weighted by the wavelength spectrum within the band of wavelengths used in a given measurement. For each scattering vector an effective wavelength is defined which, after substitution into the resolution expression developed for fixed wavelength, gives the resolution of the time-of-flight measurement. Alternatively, the resolution may be established by Monte Carlo methods. In order to check the calculated resolution function and the overall instrument resolution, measurements have been made on biological samples (myelin and collagen) which give sharp Bragg peaks at small values of scattering vector. The analysis of these results provides a direct comparison with calculations and with a similar measurement on a steady-source instrument.
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 378-386 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The accuracy of the Chebyshev expansion coefficients used for the calculation of attenuation correction factors for cylindrical samples has been improved. An increased order of expansion allows the method to be useful over a greater range of attenuation. It is shown that many of these coefficients are exactly zero, others are rational numbers, and others are rational fractions of π−1 The assumptions of Sears [J. Appl. Cryst. (1984), 17, 226–230] in his asymptotic expression of the attenuation correction factor are also examined.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 1164-1167 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 16 (1983), S. 363-369 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A pulse-shortening device is described for use on pulsed thermal-neutron sources. The device employs rotating single crystals and has applications in the design of high-resolution cold-neutron spectrometers.
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  • 6
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 589-601 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle neutron scattering instruments can be built to use either steady-state or time-of-flight techniques, although only the latter are practical at pulsed neutron sources. The techniques used to provide beams of suitable quality, wavelength range and angular collimation are considered in detail for steady-state and time-of-flight instruments at reactor neutron sources, and for time-of-flight instruments at pulsed neutron sources. For both instrument types a cold neutron source provides a definite advantage. Most, but not all, steady-state instruments use long flight paths, which can be shown to provide conditions which are optimum in many ways. However, frame overlap considerations force the use of a short flight path for time-of-flight instruments, and this in turn forces these instruments to use different collimation and beam-quality techniques from those that are usually used for steady-state instruments. Although adequate techniques now exist for building short-flight-path small-angle neutron scattering instruments, some of these short-path techniques are still developing, and can be expected to improve in the future. At present the time-of-flight instruments are more difficult to build and use, but for many experiments this difficulty is more than compensated by the large wave-vector range covered in a single measurement with such instruments.
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  • 7
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two time-of-flight powder diffractometers have operated at the Intense Pulsed Neutron Source (IPNS) since August 1981. These instruments use dedicated microcomputers to focus time-of-flight events so that data from different detectors can be summed into a single histogram. Thus, large multidetector arrays can be employed at any scattering angle from 12 to 157°. This design permits data to be collected over a uniquely wide range of d spacings while maintaining high resolution and count rates. The performance of the two instruments is evaluated by analyzing data from a standard Al2O3 sample by the Rietveld method. These instruments provide the capability for moderate- to high-resolution measurements with the duration of a typical run being a few hours.
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  • 8
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The design, development and performance of the time-of-flight (TOF) small-angle diffractometer (SAD) at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory are described. Similar TOF-SANS instruments are in operation at the pulsed neutron sources at Los Alamos National Laboratory, USA, at Rutherford Appleton Laboratory, England, and at KEK, Japan. These instruments have an advantage by comparison with their steady-state counterparts in that a relatively wide range of momentum transfer (q) can be monitored in a single experiment without the need to alter the collimation or the sample-to-detector distance. This feature makes SANS experiments easy and very effective for studying systems such as those undergoing phase transitions under different conditions, samples that cannot be easily reproduced for repetitive experiments, and systems under high temperature, pressure or shear. Three standard samples are used to demonstrate that the quality of the SANS data from SAD is comparable with those from other established steady-state SANS facilities. Two examples are given to illustrate that the wide q region accessible in a single measurement at SAD is very effective for following the time-dependent phase transitions in paraffins and temperature- and pressure-dependent phase transitions in model biomembranes.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 962-967 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The method of determining corrections to neutron time-of-flight diffraction data by Monte Carlo techniques is costly since a large range of neutron wavelengths must be considered. An optimized simulation is presented in which many wavelengths are considered simultaneously, while paths are traced only once for all wavelengths. Collision positions and scattering angles are selected from cumulative distribution functions representing all neutron wavelengths simulated. The scattered intensity is computed by weighting the simulated paths to account for the probability of their occurrence for each wavelength. The results of a calculation for a vanadium slab are given as an example.
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  • 10
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 419-424 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effect of Soller collimation on the resolution characteristics of small-angle scattering spectrometers for which there is a limitation to the total length, as in the case of a pulsed source instrument, is examined. Any finite distance between the exit of the collimation and the sample position causes the resolution of the instrument to deteriorate. This results from a correlation in angle and position for points at the sample producing an extra (cross-correlation) term in the resolution function. Expressions for this general case are derived. They are similar to those when the incident beam is defined at the sample position, except that both the source and the sample contributions have an extra term which is proportional to the finite distance between the end of the incident collimation and the sample.
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